Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, one or more magnetic disks 16, supported for rotation by a drive spindle 18 of motor 14, and an actuator 20 including at least one arm 22, the actuator being attached to a pivot bearing 24. Suspensions 26 are coupled to the ends of the arms 22, and each suspension supports at its distal end a read/write head 28. The head 28 (which will be described in greater detail with reference to FIGS. 2A and 2B) typically includes an inductive write element and a sensor read element. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 28 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to “fly” above the magnetic disk 16. Various magnetic “tracks” of information can be written to and/or read from the magnetic disk 16 as the actuator 20 causes the head 28 to pivot in a short arc across a surface of the disk 16. The pivotal position of the actuator 20 is controlled by a voice coil 30, which passes between a set of magnets (not shown) to be driven by magnetic forces caused by current flowing through the voice coil 30.
With reference now to FIGS. 2A and 2B, the head 28 includes a read element 32 and a write element 34, both of which are built upon a substrate 36 (FIG. 2B). The substrate 36 is generally constructed of a ceramic material and accounts for the majority of the head 28. The write element 34 includes a magnetic yoke 38 through which passes an electrically conductive coil 40.
With reference to FIG. 2B, the read element includes a read sensor 42, which is embedded in a dielectric medium 44 and disposed between first and second shields 46, 48. The second shield 48 also serves as a first pole of the write element 34. The read sensor 42 senses changes in a magnetic field generated by a magnetic disk 16 passing adjacent to an air bearing surface (ABS) of the head 28 defined by a plane 50.
With reference still to FIG. 2B, the yoke 38 includes the first magnetic pole 48 and a second magnetic pole 52. The first and second poles 48, 52 are joined at one end at what has been referred to as a back-gap 54. At the other end, the poles 48, 52 are separated by a write gap 56. A layer of write gap material 58 sits atop the first pole 48. The thickness of the write gap material layer 58 determines the thickness of the write gap 56, and it is formed so as not to cover the first pole at the back gap 54. A first insulation layer 60 sits atop the write gap material layer, and in addition to not covering the back-gap 54, is formed to leave a portion of the write gap material layer 58 uncovered near the ABS plane 50.
With reference still to FIG. 2B, the conductive coil 40 is formed atop the first insulation layer 60. As can be seen with reference to FIG. 2A, the coil 40 extends beyond the edges of the yoke 38 and wraps around the back gap. The coil 40 includes a pair of contact pads 62, which are useful for applying an electric potential to cause an electrical current to flow through the coil 40. A second insulation layer, sometimes referred to as a “coil insulation layer” 64, covers the coil 40, insulating it from the second pole 52 as well as insulating the windings of the coil 40 from one another.
With reference still to FIG. 2B, when a current is caused to flow through the coil 40, a magnetic flux is induced in the yoke 38. This magnetic flux is interrupted by the write gap 56, which generates a magnetic field that fringes out from the write gap. This fringing magnetic field can be used to impart a magnetic data signal on a disk 16 passing thereby.
FIG. 2C is a cross sectional illustration of the head 28 in an intermediate stage of development. In order to form the coil 40 a seed layer of a conductive material must first be applied. The seed layer 66 is a very thin layer, preferably of copper, that provides a conductive base upon which the coil may be electroplated. Also, a mask 68 must be applied to the structure. This mask is usually constructed of a positive photoresist which is spun on and then patterned using photolithography. The photolithographic process involves exposing the photoresist to radiation in the desired coil pattern. The portions of the photoresist exposed to the radiation become hardened, while the unexposed portions do not and can later be washed away leaving the desired mask structure.
In order to ensure that the mask 68 maintains adhesion to the seed layer 66, the wafer must be baked. This baking step has become more important as heads have become smaller in an effort to decrease track width, and increase data density. The baking step involves heating the wafer to a temperature of 120 to 130 degrees Celsius. While this post develop baking process, initially used to harden printing plate photoresist, a similar baking process has subsequently been used to improve the performance of Diazoquinone-novolak (DQN) photoresist. Post develop bake process involves the thermochemical (thermolysis) reactions of the resin, sensitizer, and residual solvents with heat and air. Post develop bake removes most of the water molecules that are absorbed by the DQN photoresist films after developing and rinsing. With a baking temperature of 120 to 150 degrees Celsius, solvents and water molecules can be removed to improve the bonding between photoresist and substrate. It also reduces side effects in post processes. Furthermore, thermal stabilization can be achieved with intermolecular reactions between sensitizer and the resin. Plastic flow may occur with increasing bake temperature as inter difflusion between a silyated surface primer and the photoresist. The plastic flow overcomes the surface adhesive force, surface tension and the internal modulus force of the photoresist. The photoresist profile starts to round at corners and eventually the photoresist starts to flow with increasing bake temperature.
Unfortunately, as can be seen in FIGS. 2B and 2C, this baking step causes the photoresist to shrink, which results in a shallow wall angle 70 especially at the outermost turn of the coil pattern. This shallow wall angle results in a poorly defined coil 40 having a poorly defined, shallow wall angle at its outer edge 72 as can be seen in FIG. 2B. This shallow wall angle at the outer edge 72 of the coil 40 not only results in poor coil definition, but also leads to poor topography of the later applied second insulation layer 64 and second pole 52 (FIG. 2B). After the second pole has been constructed, the wafer is cut along line 74FIG. 2C) to provide the ABS surface of plane 50 (FIG. 2B).
Therefore there remains a need for a method for manufacturing a write element that prevents the shallow wall angle formation on the coil. The method would preferably involve as few additional process steps as possible and would also allow a post develop bake to be employed for mask processing purposes.